The present invention concerns a method and a device for cleaning and disinfecting treatment of water, during which the water is subjected to an electric field.
During such methods that are currently known, a current is normally lead through the water that is to be treated, which leads to various electrochemical reactions in the water. In this way ionic compounds, such as salts dissolved in the water that are often added in association with the cleaning/disinfecting, are dissociated, furthermore, ions can be released from either or both of the electrodes, and the water itself can be decomposed into hydrogen gas and oxygen gas at the cathode and the anode, respectively. These reactions, and the current itself, have a killing effect on various micro-organisms in the water. Furthermore, the ionisation can lead to the aggregation of colloid particles and suchlike, which thus become easier to remove from the water.
An example of prior art of said kind is described in WO 86/01543: An electrode device for cleaning water in swimming pools has at least one copper electrode, and the current that is led between the electrodes is reversed at defined intervals. The only intervals of which examples are given are 22 and 25 seconds long. It is specified that the electrodes should be manufactured of a material that resists electrolysis. WO 86/01543 makes it also clear that silver must be added in cases where one wishes to combat micro-organisms such as coli bacteria in the swimming pool, for example by having one of the electrodes manufactured of silver or a combination of silver and copper. The device according to WO 86/01543 is fed with rectified current of a current strength that is not specified, and the time interval is regulated by an integrated time-control circuit of type LM 555.
It is desired in this context to achieve a technique of the aforementioned type that does not depend on the electrolysis of dissolved salts or the release of metal from the electrodes in order to achieve cleaning/disinfecting, in particular to avoid the use of silver, since not only is it well known that silver compounds are toxic also for humans, but also it clearly involves a significant cost, since silver usually commands a high price.
The present invention, which is defined by the attached claims, offers the possibility of fulfilling this desire. To be more precise, the present invention concerns a method for cleaning and disinfecting treatment of water, during which the water is subjected to at least one electric field by which the electric field is a low-current field with pulsating direct voltage. No silver is added to the water during the method, neither in the form of silver metal nor silver salts. The polarity of the low-current field is reversed at previously defined time intervals, which are up to about 20 seconds long.
One advantage of the method according to the invention is that it does not depend on the presence of substances dissolved or dispersed in the water, and thus the method is directly suitable for use on brackish water and fresh water. The effect of the methods can, however, be reinforced by the addition of, or the previous presence of, suitable substances.
The term xe2x80x9clow-current fieldxe2x80x9d is used in the present application to denote an electric field through which either no current or only low currents flow, whereby xe2x80x9clow currentxe2x80x9d means, in agreement with SFS 1958:588, that the electric current does not have such a voltage, current strength or frequency that it can constitute a danger for people, pets or property. The maximum current strength of the electric field is preferably about 1 A, and its maximum voltage is preferably about 40 V. It should, however, be pointed out that the method is also effective in cases where the conducting element or elements that define the field do not exchange charge with the water. Thus the conducting elements that are used according to the invention can be essentially electrically insulated from the water, for example, by encasing those parts of the conducting elements that are placed in the water in an electrically insulating material, such as a plastic material. xe2x80x9cConducting elementxe2x80x9d should be understood here to denote an element that includes conducting material, but not necessarily an element that conducts an electrical current through the water. It is, on the other hand, preferable that a current does exist, that is to say, that the conducting elements are electrodes, whereby the method preferably includes an electrolytic reaction in the water.
xe2x80x9cPulsatingxe2x80x9d in the expressions xe2x80x9cpulsating direct voltagexe2x80x9d and xe2x80x9cpulsating direct currentxe2x80x9d is used here to denote that the voltage/current occurs in pulses, such that the pulses are divided from each other by periods in which the voltage/current takes the value 0 or values close to 0. The pulses can have various shapes, for example, sawtooth, square, triangular or clipped sine waves such as those that are normally obtained when alternating current is rectified by means of a half- or full-wave rectifier. As has been specified above, the direct voltage/direct current can be made to change direction after a previously determined time period, which thus means that the direct voltage/direct current passes in only one direction during this period.
In one embodiment of the present invention, the electrical low-current field exists between two or more conducting elements, which are at least partly submerged in the water, whereby the conducting elements are preferably electrodes between which there flows a pulsating direct current with a current strength of a maximum of about 1 A.
In another embodiment of the present invention, the electrical low-current field is generated by electrical induction in one or several conducting elements that are located in a rectified pulsating magnetic field, whereby the conducting elements are at least partly submerged in the water. The pulsating magnetic field can be brought to change direction after a previously determined time period which is up to about 20 seconds long, which thus results in the electrical low-current field also changing direction.
The present invention also concerns a device for the realization of the first embodiment of the method according to the invention, in which the electrical low-current field exists between two or more conducting elements, which device includes:
a source of pulsating direct voltage
two or more conducting elements, which are connected in a conducting manner to the source of pulsating direct voltage and which arc arranged to produce a low-current field with pulsating direct voltage between them; and
means of changing in a time-dependent manner the direction of the pulsating direct voltage.
The source of pulsating direct voltage can be a conventional rectifier, for example of a half- or full-wave type, or it can be of the type that exists in the ignition systems of internal combustion motors. It can also consist of a mechanical or electronic device, or a combination of these, for conversion of a steady direct voltage to a pulsating one, for example, a relay or pilot switch suitable for the purpose.
The conducting elements lack any significant ability to release silver during the use of the device, and it is preferable that they do not contain any significant amounts of silver, On the other hand, they can contain or consist of copper or a copper alloy; steel or a steel alloy, preferably stainless steel; carbon, preferably in the form of graphite; or a combination of several of these materials.
The device is preferably arranged to create a low-current field of a maximum of 1 A between the conducting elements.
The device for changing the pulsating direct voltage in a time-dependent manner can consist of one or several mechanical or electronic devices, or combinations of these, for a regulation of the polarity of the current circuit in a time-dependent manner, which device may be of a per se known type.
Furthermore, the present invention also relates to a device for realization of the second embodiment of the method according to the invention mentioned above, that is, the embodiment in which the electrical low-current field is produced by electromagnetic induction in one or several conducting elements that are located in a rectified pulsating magnetic field, which device includes:
a source of a rectified pulsating magnetic field; and
one or more conducting elements that is/are arranged in the pulsating magnetic field such that, when the device is in use, an electric field is produced around the conducting element or elements by electromagnetic induction.
This device preferably includes a vessel or pipe that is intended during use of the device to hold, or be flowed through by, the water that is to be cleaned/disinfected, whereby the source of the pulsating magnetic field is arranged outside of the vessel or pipe and the conducting element is arranged inside of it.
The source of the rectified pulsating magnetic field can consist of a winding of wires of conducting material, which winding can surround the conducting element or elements, or it may surround a preferably ring-shaped core of magnetic conducting material preferably containing iron, which in turn surrounds the conducting element or elements, whereby a pulsating direct current flows through the winding, which pulsating direct current can be generated by a conventional rectifier, for example, of a half- or full-wave type, or achieved in a manner equivalent to that used in the ignition systems of internal combustion motors. The pulsating direct current can also be achieved with the aid of a mechanical or electronic device, or a combination of these, for conversion of a steady direct current to a pulsating direct current.
The conducting element or elements lack any significant ability to release silver during use of the device, and it is preferable that it/they do not contain any significant amounts of silver. On the other hand, it/they can contain or consist of copper or a copper alloy; steel or a steel alloy, preferably stainless steel; carbon, preferably in the form of graphite; or a combination of several of these materials.
The device is preferably arranged to produce a low-current field with a maximum strength of 1 A between the conducting elements.
The device for changing in a time-dependent manner the direction of the pulsating magnetic field may consist of a mechanical or electronic device, or a combination of these, for time-dependent regulation of the polarity of a current circuit, which device may very well be of a known type, for example, a relay or pilot switch that is suitable for the purpose, whereby the device is arranged to act on the pulsating direct current that provides input for the source of the rectified pulsating magnetic field.